This application is based on applications Nos. 2000-331415, 2001-020625, 2001-020626, and 2000-362019 filed in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a photoelectric conversion device used for solar power generation.
2. Description of the Related Art
Photoelectric conversion devices using crystalline semiconductor particles have been known as prior art(Refer to U.S. Pat. No. 4,514,580 as an example).
In the above photoelectric conversion device using crystalline semiconductor particles, an aluminum electrode layer with a low melting point and large electric conductivity is used in the area where the substrate and the crystalline semiconductor particles are joined together. Accordingly, it is possible to accomplish low temperature joining and formation of a low resistance electrode. In addition, the device has another advantage when using p-type crystalline semiconductor particles that p+ regions can be formed in the junctions between the semiconductor particles and the aluminum electrode layer so that high conversion efficiency can be achieved.
However, in the arrangement described above, fusion bonding proceeds between the crystalline semiconductor particles and the aluminum electrode layer without restriction making it hard to control the joining.
As an effective joining-control means, there has been an idea that the fusion bonding is prevented from proceeding beyond the thickness of the aluminum electrode layer by disposing a metal layer that has a melting point higher than that of aluminum beneath the aluminum layer. This high melting point metal may be iron or stainless steel, which is optimum in terms of melting point, rigidity, thermal expansivity and cost performance.
The above U.S. Pat. No. 4,514,580 discloses an arrangement shown in FIG. 9 in which an aluminum film 12 is formed around a steel substrate 11, and crushed p-type silicon particles 13 are joined to the aluminum film 12, over which an insulator layer 16, a n-type silicon layer 14, and a transparent conductive layer 15 are formed in succession.
However, in the above arrangement, it is necessary to apply heat at a high temperature above 550xc2x0 C. when joining the silicon and the aluminum together. In such a high temperature range, aluminum and iron react to each other so that an aluminum-iron alloy layer is generated in the interface between the aluminum and iron. Such an aluminum-iron layer is so hard that it tends to generate cracks, which causes the reliability of the photoelectric conversion device to drop.
The present invention intends to suppress the reaction between the aluminum electrode layer and the substrate so as to maintain the high adhesiveness of the aluminum electrode layer, thereby providing a photoelectric conversion device with high reliability.
Also, there has been a problem that when the aluminum electrode layer provided at the joint between the substrate and the crystalline semiconductor particles is too thin, it is likely to be oxidized and suffer corrosion when tested under a high temperature-high humidity environment resulting in lowered reliability.
In order to solve this problem, the aluminum electrode layer needs to be thickened. However, when the aluminum electrode layer is thickened, the particle sizes of the crystalline semiconductor particles to be joined need to be increased accordingly, which leads to the problem of lowering of the photoelectric conversion efficiency.
It is an object of this invention to suppress excessive reaction between the aluminum electrode layer serving as the substrate and the crystalline semiconductor particles and provide a low-cost photoelectric conversion device with high efficiency in which miniaturization of the silicon particles and thinning of the aluminum electrode layer can be accomplished.
(1) A photoelectric conversion device according to the present invention comprises a substrate having an electrode layer of one side, numerous crystalline semiconductor grains deposited on the substrate, an insulator formed among the crystalline semiconductor grains, and another electrode layer connected to the upper portions of the crystalline semiconductor grains. The substrate has a layered structure which includes: the electrode layer of one side, an intermediate layer and a base material layer. The electrode layer comprises an aluminum layer or an aluminum alloy layer. The intermediate layer comprises an alloy composed of one or a plurality of elements selected from among nickel, titanium, chromium, and cobalt(claim 1).
The structure above may be arranged such that the intermediate layer serves also as the base material layer(claim 2).
According to the above arrangement, it is possible to suppress the reaction between the aluminum electrode layer and the base material layer so as to maintain the high adhesiveness of the aluminum electrode layer. Accordingly, a photoelectric conversion device with high reliability and high conversion efficiency can be obtained.
(2) Another photoelectric conversion device according to the present invention comprises a substrate having an electrode of one side, numerous crystalline semiconductor grains deposited on the substrate, an insulator formed among the crystalline semiconductor grains, and another electrode layer connected to the upper portions of the crystalline semiconductor grains. The electrode layer of one side comprises an alloy composed of aluminum and silicon(claim 3).
According to this arrangement, it is possible to suppress excessive fusion bonding reaction between the aluminum electrode layer and the crystalline semiconductor grains so as to maintain the strength required for the substrate. Accordingly, it is possible to prevent corrosion from occurring on the surface of the substrate, thereby obtaining a photoelectric conversion device with high reliability and high conversion efficiency.
(3) Another photoelectric conversion device according to the present invention comprises a substrate having an electrode layer of one side, numerous crystalline semiconductor grains deposited on the substrate, an insulator formed among the crystalline semiconductor grains, and another electrode layer connected to the upper portions of the crystalline semiconductor grains. The electrode layer of one side comprises an alloy composed of aluminum and one or a plurality of elements selected from among magnesium, manganese, chromium, and titanium(claim 5).
Similarly to the case of (2) above, excessive fusion bonding reaction between the aluminum electrode layer and the crystalline semiconductor grains can be suppressed by this arrangement. Corrosion on the surface of the substrate can therefore be prevented from occurring, and as a result, a photoelectric conversion device with high reliability and high conversion efficiency can be obtained.
(4) Another photoelectric conversion device according to the present invention comprises a substrate having an electrode layer of one side, numerous crystalline semiconductor grains deposited on the substrate, an insulator formed among the crystalline semiconductor grains, and another electrode layer connected to the upper portions of the crystalline semiconductor grains. A junction between the crystalline semiconductor grains and the electrode layer of one side includes an alloy formed therein. The alloy is composed of the semiconductor of the crystalline semiconductor grains and a metal constituting the electrode layer of one side, and the alloy has particles of the semiconductor material of the crystalline semiconductor grains being dispersed therein(claim 6).
According to this arrangement, since the junctions comprise complexes including particles dispersed therein that comprise the material constituting the crystalline semiconductor grains, the thermal expansion coefficient of the complexes is an intermediate value between those of the crystalline semiconductor grains and the substrate, so that cracks due to stress caused by the difference in thermal expansion coefficient can be prevented from occurring in the junctions. Accordingly, the substrate and the crystalline semiconductor grains can be joined in a good condition.
Structural details of the present invention will be hereinafter described referring to the drawings.